That is not a discount, by any stretch.I'd say they are manipulating the buyer into paying a premium for lesser demand ( read as unslabbable) copies, in one fell swoop.
That is the oldest trick in the book, when it comes to moving off lesser grade books, in one shot.
They take a set of 66 issues, none of which would really justify grading fees, and jack the price as high up as can be....and then advertise a "40% off clearance discount".
They know that they have a wide enough of a cutomer base , that they will be able to capitalize on a sucker who has money to burn and....whammo-they rake in a thousand dollars(or whatever the price is on the set) for straightup mid grade/reader copies of books that would be difficult , and would take a long amount of waiting time, to move individually.
I thought I had made my sarcasm clear, but I always forget that it's not always clear on the internet.
Chuckles could offer 90% off his ludicrous prices here and still be well over FMV.